New research published on Wednesday, however, shows the
extreme, emaciating diet doesn't increase lifespan in rhesus
monkeys, the closest human relatives to try it in a rigorous,
long-running study. While caveats remain, outside experts
regarded the findings as definitive, particularly when combined
with those from a similar study.

"If there's a way to manipulate the human diet to let us
live longer, we haven't figured it out yet and it may not
exist," said biologist Steven Austad of the University of Texas
Health Science Center's Barshop Institute for Longevity and
Aging Studies, who wrote an analysis of the study in Nature.

Since 1934, research has shown that lab rats, mice, yeast,
fruit flies and round worms fed 10 percent to 40 percent fewer
calories than their free-eating peers lived some 30 percent
longer. In some studies, they lived twice as long.

Such findings have spawned a growing community of believers
who seek better health and longer life in calorie-restricted
(CR)diets, as promised in the 2005 book "The Longevity Diet,"
including 5,000 members of the CR Society International. The
research has also prompted companies like Procter & Gamble
and Nu Skin Enterprises to develop drugs to mimic
the effects of calorie restriction.

The new study, from the National Institute on Aging, part of
the U.S. National Institutes of Health, suggests a surprising
disconnect between health and lifespan. It found that most of
the 57 calorie-restricted monkeys had healthier hearts and
immune systems and lower rates of diabetes, cancer or other ills
than the 64 control monkeys. But there was no longevity pay-off.

"You can argue that the calorie-restricted animals are
healthier," said Austad. "They have better cholesterol profiles,
less muscle loss, less disease. But it didn't translate into
greater longevity. What we learn from this is you can un-link
health and longevity."

YOUNGER IMMUNE SYSTEMS, LESS HEART DISEASE

The NIA study, launched in 1987, is one of two investigating
whether eating just 70 percent of the calories in a standard lab
diet extends life in a long-lived primate. The Wisconsin
National Primate Research Center's study, begun in 1989, also
uses rhesus monkeys, whose physiology, genetics and median
lifespan (27 years) are closer to humans than are the rodents in
earlier calorie-restriction research.

Initial results were promising. In 2006 the NIA group
reported that calorie-restricted monkeys had younger-seeming
immune systems. Wisconsin reported that after 20 years of eating
like birds, the monkeys were less likely to get heart disease,
diabetes, cancer and other diseases of aging.

They also lived longer: By 2009, 80 percent of the
free-eating Wisconsin monkeys had died of age-related illness,
but only 50 percent of calorie-restricted monkeys had. Those
findings, the scientists reported at the time, showed "that CR
slows aging in a primate species."

Experts on aging have since waited for the NIA to weigh in,
and the verdict was a shock: "The calorie-restricted monkeys
lived no longer than the other monkeys," NIA's Julie Mattison,
who helped lead the study, told Reuters.

The oldest animals in each group had the same incidence of
tumors, heart disease and general deterioration. While the
abstemious monkeys had some improved health markers such as
cholesterol and triglyceride levels, Mattison said, "that didn't
translate into better survival."

The NIA study showed that even monkeys starting calorie
restriction early in life, from 1 to 14 years of age, had no
lifespan edge over their gourmand peers. With 19 of the 40
monkeys whose eating was restricted starting in youth still
alive, the NIA scientists calculated, the chance that they will
outlive free-eating monkeys is less than one-tenth of 1 percent.

Perhaps more surprising, health markers were often worse in
monkeys that began calorie restriction as young adults than
older ones, the opposite of what scientists expected. And more
of the animals that started calorie restriction when young died
of causes unrelated to aging than did their free-eating peers.
"There may be something about calorie restriction that makes
animals more susceptible to death from other causes," said
Austad.

A KILLER CONTROL GROUP

Scientists offered several explanations for why the NIA's
findings differ from more encouraging results in the Wisconsin
study.

The Wisconsin monkeys' diet had seven times the table sugar
(28 percent of calories, like Americans' diets) as the NIA's (4
percent). The Wisconsin control monkeys also ate however much
they wished; the NIA control monkeys ate a fixed amount and, as
a result, weighed less.

That suggests the longevity diet didn't really extend
lifespan in the Wisconsin monkeys: It only seemed to because the
control monkeys ate themselves into an early grave.

"Comparing calorie restriction to what you think is a normal
diet but is in fact an unhealthy diet with too much food and too
much sucrose can trip you up," said Austad. "If you keep your
control animals to a healthy weight, as the NIA did, a diet that
produces extreme emaciation has no further effect on longevity."

Most problematic, many of the Wisconsin study's
calorie-restricted monkeys died of causes unrelated to aging,
such as anesthesia used in some experiments and gastrointestinal
bloat.

Only by not counting those deaths did the Wisconsin
scientists find a statistically significant longevity effect,
said Wisconsin's Ricki Colman, a leader of that study.

It is too soon to know how the NIA study will affect the
development of drugs aimed at replicating calorie restriction's
benefits without the hunger pangs. They include mannoheptulose,
a compound derived from unripe avocados that "tricks cells into
thinking they ate less," said George Roth, CEO of privately held
GeroScience.

Roth helped launch the NIA study and is a co-author of the
new paper. He believes there is still good evidence in favor of
calorie restriction, including the Wisconsin study's findings.
GeroScience is working with Procter & Gamble to use
mannoheptulose as a lifespan-increasing supplement for dogs and
hopes to raise money for a clinical trial in people.

LifeGen Technologies, co-founded by a leader of the
Wisconsin study, has tested a compound that mimicked some
genetic changes seen with calorie restriction in rodents. In
2001, the company was bought by Nu Skin, which "utilizes the
research data generated from caloric restriction studies to
assist in its development of nutritional supplements," a
spokeswoman said.

The NIA and Wisconsin teams are continuing to collect data
to see if calorie restriction suddenly proves more beneficial.
"But what I take away from these studies is that extreme
emaciation may not be the correct paradigm," said University of
Texas biologist Austad. "If I were them (companies or scientists
banking on this), I'd be worried."